The fact was Priestley could not keep away from his laboratory.
“Having acquired a fondness for experiments, even slighter inducements than I have had would have been sufficient to determine my conduct.”
The preface is noteworthy for its plea for the position of experimental science in the scheme of general education.
“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”
In the course of some observations on the effect “of impregnating oil of vitriol with nitrous acid vapour” he discovered nitrosulphuric acid, the so-called “Leaden Chamber Crystals,” whose properties and behaviour with water he describes with accuracy and even eloquence. Of these crystals he says: “A more beautiful appearance can hardly be imagined, and I am afraid I shall never see the like again.” He also noticed the formation of the dark brown compound which nitric oxide forms with a solution of green vitriol, and adds:—
“To determine whether the phenomena attending the impregnation of the solution of green vitriol with nitrous air depended in any measure upon the seeming astringency of that solution ... I impregnated a quantity of green tea, which is also said to be astringent, with nitrous air, but no sensible change of colour was produced in it.”
He several times noticed the deep blue liquid which nitrogen peroxide forms with cold water. He made many attempts to use nitric oxide as an antiseptic, especially for culinary purposes. But the gastronomic results with fowls and pigeons were not to his liking, although he says, “my friend Mr Magellan ... had not so bad an opinion of this piece of cookery as I had.” One cannot read Priestley’s description of his multifarious experiments without being struck with the number of occasions in which he just missed making discoveries of first-rate importance. It is obvious that he had obtained chlorine without recognising it, even before the news of Scheele’s discovery reached this country. He had also prepared, without knowing it, phosphoretted hydrogen and phosphorous acid. At times, however, he can follow a clue with remarkable perspicacity; as in his observation of the cause of the “flouring” of mercury, and in his discovery of a method of removing lead and tin from that metal.
The subject of “dephlogisticated air” naturally continued to interest him, and he again returns to it in this volume, for he says:—
“As it sometimes amuses myself it may perhaps amuse others to look back with me to the several steps in the actual progress of this investigation, some of which I overlooked in my last account of it.”
He points out, as already stated, that he must have had the new gas in his hands as far back as November 1771, having obtained it from nitre. He admits that he had no particular view in making his crucial experiment of August 1, 1774,